1. Field of the Invention
The present invention relates to an ink jet recording apparatus used in a printer or the like for drawing characters and patterns by discharging liquid such as ink from tiny nozzles, and forming a liquid pattern on recording paper or sheet, and its manufacturing method.
2. Related Art of the Invention
Recently, as a printing device of a personal computer, the printer using an ink jet recording apparatus is widely used owing to its ease of handling, excellent printing performance, and low cost. The ink jet recording apparatus is available in various types, including a type of generating foams in ink by heat energy, and discharging ink drops by the pressure wave by the foams, a type of sucking and discharging ink drops by electrostatic power, and a type of making use of pressure wave by oscillator such as piezo element.
Generally, a type using a piezo element is composed of, for example, an ink feed chamber communicating with an ink nozzle, a pressure chamber communicating with this ink feed chamber, and a diaphragm combined with the piezo element, provided in this pressure chamber. Conventionally, the ink discharge direction and the vibrating direction of the piezo element were the same. In such constitution, when a specified voltage is applied to the piezo element, the piezo element is expanded or contracted, and a drum-like vibration occurs between the piezo element and diaphragm, and the ink in the pressure chamber is compressed, so that the ink liquid drops are discharged from the ink nozzle.
Incidentally, the work load W of the piezo element is Wxe2x88x9dEpxc2x7d312 (V/t)2"ugr"p, (where Ep: Young""s modulus of piezo element, d31: piezoelectric constant of the piezo element, V: voltage applied to the piezo element, t: thickness of the piezo element, and "ugr"p: volume of the piezo element), and as the nozzle density is raised (the width of the pressure chamber is narrowed), the value of "ugr"p becomes smaller. Therefore, to obtain a work load necessary for discharging the ink, it is necessary to reduce the thickness of the piezo element, and heighten the withstand voltage of the piezo element. However, the piezo element used in the conventional ink jet head was a thick film or bulk, and it was difficult to achieve both thin film of piezo element and high withstand voltage. Hence, when the volume of the piezo element is decreased, the displacement of the diaphragm due to the piezo element becomes smaller, and sufficient discharge force is not obtained. On the other hand, if it is attempted to increase the displacement by increasing the work load W, it is difficult to realize small multi-nozzle head, high density of multi-nozzle or long length of the head, and it was difficult to achieve both small size of head and high recording speed. More specifically, in the conventional piezo element of thick film or bulk, the limit of the nozzle density was 2 to 3 nozzles/mm.
Accordingly, to solve the problems, for example, as disclosed in Japanese Patent Application No. 6-273650, the diaphragm is designed to vibrate in a direction vertical to the vibrating direction of the piezo element, and a small vibration caused by the piezo element is amplified to a large vibration, so that the displacement is increase in a same size, or in other proposal, a counter electrode is provided at a position opposite to the ink nozzle, a specified high voltage, for example, about 1.5 kV is applied between the counter electrode and the ink in the pressure chamber, and the ink is expanded to the counter electrode side (that is, the sheet or recording medium side) by its electrostatic power, so that the ink may be discharged by applying on a small pressure.
In such conventional ink jet recording apparatus, however, while a voltage is applied to the counter electrode so that the ink may be easily discharged by a small pressure, the ink is advanced to the leading end of the nozzle, and the ink droops from the leading end of the ink nozzle. To prevent ink drooping, alternatively, when the leading end of the nozzle is composed of a metal member (see FIG. 2(a); detail described later), the ink injecting speed is lowered, or to the contrary, when the leading end of the nozzle is composed of an insulator for increasing the ink injecting speed (see FIG. 2(b); detail described later), the ink droops, and owing to these contradictory problems, it was hard to increase the nozzle density, and in the case of multi-nozzle head by downsizing, crosstalk between nozzles occurs.
In consideration of the problems of such conventional liquid drop discharge device, it is an object of the invention to present an ink jet recording apparatus capable of preventing drooping of the ink from the leading end of the ink nozzle, increasing the nozzle density, and suppress the crosstalk between nozzles.
An ink jet recording apparatus of the claim 1 comprises a pressure chamber for accommodating an ink liquid, a nozzle communicating with this pressure chamber for discharging said ink liquid, and pressure applying means for applying a pressure to said pressure chamber,
wherein said pressure applying means includes a diaphragm formed in said pressure chamber, and a piezoelectric element made of a monocrystalline or polycrystalline piezoelectric member highly oriented along a polarization axis showing perovskite structure, mainly composed of lead zirconate titanate or barium titanate, for vibrating the diaphragm, and a specified voltage is applied at least to said piezoelectric element when discharging said ink liquid into a recording medium disposed at the front side of said nozzle.
An ink jet recording apparatus of claim 3 comprises a pressure chamber for accommodating an ink liquid, a nozzle communicating with this pressure chamber for discharging said ink liquid, and pressure applying means for applying a pressure to said pressure chamber,
wherein said pressure applying means includes a diaphragm formed in said pressure chamber, and a piezoelectric element made of a piezoelectric member such as LiNbO3 or LiTaO3, for vibrating the diaphragm, and a specified voltage is applied at least to said piezoelectric element when discharging said ink liquid into a recording medium disposed at the front side of said nozzle.
An ink jet recording apparatus of claim 4 comprises a first pressure chamber for accommodating an ink liquid, first pressure applying means for applying a pressure to this first pressure chamber, plural second pressure chambers communicating with said first pressure chamber having nozzles for discharging said ink liquid individually, and second pressure applying means for applying a pressure to each one of said plural second pressure chambers,
wherein discharge and stopping of discharge of said ink liquid into a recording medium disposed at the front side of said nozzle are controlled by adjusting the applied pressure to said first pressure chamber by said first pressure applying means and the applied pressure to said second pressure chambers by said second pressure applying means.
As constituted herein, by independently controlling application of pressure by two pressure applying means, swelling of the ink liquid at the nozzle is uniform. Or if the fluctuations of the applied pressure by the pressure applying means are large, the effects are small. As a result, it is easy to realize higher density of nozzle heads, multiple nozzles, and smaller size.
An ink jet recording apparatus of claim 8 comprises an ink liquid chamber for accommodating an ink liquid, a nozzle communicating with this ink liquid chamber for discharging said ink liquid, and pressure wave generating means for injecting a pressure wave to said ink liquid chamber,
wherein said pressure wave generating means includes a diaphragm formed in said ink liquid chamber, and a piezoelectric element for vibrating the diaphragm, and a specified high frequency voltage is applied at least to said piezoelectric element when discharging said ink liquid into a recording medium disposed at the front side of said nozzle.
In this constitution, the voltage applied to the piezoelectric element can be lowered, so that the nozzle head may be reduced in size.
The invention as set forth in claim 11 relates to a manufacturing method of an ink jet recording apparatus characterized by forming an individual electrode on a MgO substrate, forming a monocrystalline layer or polycrystalline layer having an orientation property showing perovskite structure, mainly composed of lead titanate zirconate or barium titanate, on this individual electrode, forming a common electrode on this monocrystalline layer or polycrystalline layer, forming a diaphragm made of a material comprising Ni, Cr, or zirconia on this common electrode, forming a pressure chamber for accommodating an ink liquid on this diaphragm, and removing the MgO substrate by etching, thereby fabricating pressure applying means for applying a pressure to the pressure chamber.
Such process is a manufacturing process of semiconductor, and hence higher density of nozzle heads, multiple nozzles, and longer size may be realized.
A manufacturing method of ink jet recording apparatus of claim 12 is characterized by forming a diaphragm on a specified surface of a pressure chamber for accommodating an ink liquid, integrally with said pressure chamber by an Si member, forming a common electrode on said diaphragm, coupling directly SiO2 formed on this common electrode with LiNbO3 or LiTaO3, and forming an individual electrode further on this LiNbO3 or LiTaO3, thereby fabricating pressure applying means for applying a pressure to said pressure chamber.
Thus, by directly coupling the SiO2 formed on the common electrode with LiNbO3 or LiTaO3, the piezoelectric effect is enhanced.